Certain autostereoscopic displays, sometimes referred to as automultiscopic displays, provide multiple views of the same scene, rather than only a left and a right view. This allows the viewer to assume multiple positions in the viewing cone, i.e., move left-right in front of the display, while still obtaining a stereoscopic perception of the scene.
However, not all positions assumed by the viewer are equally suitable for obtaining stereoscopic perception of the scene. In particular, when the display is arranged for repeating the viewing cone as a series of viewing cones, a viewer may be positioned such that, e.g., the left eye perceives an outermost right-hand view of a given viewing cone, and the right eye perceives an outermost left-hand view of an adjacent viewing cone. There the viewer is positioned at a cone transition. At such a viewing position, a viewer obtains a so-termed pseudoscopic perception of the scene, in which the scene often appears to have a depth, yet which is incorrect. Pseudoscopic perception is known to cause headaches and other symptoms of visual strain.
Despite the aforementioned visual strain caused by pseudoscopic perception, it is not always obvious to the viewer that he is positioned at a pseudoscopic viewing position.
U.S. Pat. No. 6,055,013 discloses an autostereoscopic display providing four views in each lobe, i.e., in each viewing cone. It is said that an observer has a wide range of viewing freedom with pseudoscopic viewing positions being present at the boundaries between adjacent lobes. A technique is illustrated for providing an observer with a visual indication of the pseudoscopic positions. For that purpose, a parallax optic is arranged for providing an indication in a central lobe that is dark whereas the indication in adjacent lobes is bright. The next lobes are then again dark, and so on. Thus, at pseudoscopic viewing positions, at least one eye of the observer sees a non-black position indication. The technique of U.S. Pat. No. 6,055,013 thus allows an observer to distinguish between desired stereoscopic viewing positions and undesirable pseudoscopic viewing positions.
US 2004/0252187 describes a front projection display that is able to segment the viewer space into segments by using time sequential multiplexing. Each of the segments receives a different full resolution image stream. The system combines a pixel generation mechanism with an array of rotating micro mirrors that sweeps the pixels through the user space to provide an operation mode for autostereoscopic 3D. The system has a viewer detector that determines the positions of the users relative to the screen, the positions being achieved with head tracking. The positional data is used to render customized views for each specific user. Hence the system produces a number of sequential view perspectives based on the position of users relative to the screen. In addition a “fall-back” scenario is described for the case that no users are identified.